The director died Monday night at a Los Angeles Hospital, Joshua Astrachan, a producer at Altman's Sandcastle 5 Productions in New York City, told The Associated Press. He died from complications due to cancer, Sandcastle 5 Productions said in a statement.
A five-time Academy Award nominee for best director, most recently for 2001's "Gosford Park," he finally won a lifetime achievement Oscar in 2006.
"No other filmmaker has gotten a better shake than I have," Altman said while accepting the award. "I'm very fortunate in my career. I've never had to direct a film I didn't choose or develop. My love for filmmaking has given me an entree to the world and to the human condition."
Garrison Keillor, who starred in Altman's last movie -- this year's "A Prairie Home Companion" -- said Tuesday that Altman's love of film clearly came through on the set.
"Mr. Altman loved making movies. He loved the chaos of shooting and the sociability of the crew and actors -- he adored actors -- and he loved the editing room and he especially loved sitting in a screening room and watching the thing over and over with other people," Keillor said in a statement to The Associated Press. "He didn't care for the money end of things, he didn't mind doing publicity, but when he was working he was in heaven."
Elliot Gould, who starred in "M-A-S-H," said Altman's legacy would "nuture and inspire filmmakers and artists for generations to come."
"He was the last great American director in the tradition of John Ford," Gould said. "He was my friend and I'll always be grateful to him for the experience and opportunities he gave me."
Altman had one of the most distinctive styles among modern filmmakers. He often employed huge ensemble casts, encouraged improvisation and overlapping dialogue and filmed scenes in long tracking shots that would flit from character to character.
Perpetually in and out of favor with audiences and critics, Altman worked ceaselessly since his anti-war black comedy "M-A-S-H" established his reputation in 1970, but he would go for years at a time directing obscure movies before roaring back with a hit.
After a string of commercial duds including "The Gingerbread Man" in 1998, "Cookie's Fortune" in 1999 and "Dr. T & the Women" in 2000, Altman took his all-American cynicism to Britain for 2001's "Gosford Park."
A combination murder-mystery and class-war satire set among snobbish socialites and their servants on an English estate in the 1930s, "Gosford Park" was Altman's biggest box-office success since "M-A-S-H."
Besides best-director, "Gosford Park" earned six other Oscar nominations, including best picture and best supporting actress for both Helen Mirren and Maggie Smith. It won the original-screenplay Oscar, and Altman took the best-director prize at the Golden Globes for "Gosford Park."
Altman's other best-director Oscar nominations came for "M-A-S-H," the country music saga "Nashville" from 1975, the movie-business satire "The Player" from 1992 and the ensemble character study "Short Cuts" from 1993. He also earned a best-picture nomination as producer of "Nashville."
No director ever got more best-director nominations without winning a regular Oscar, though four other men -- Alfred Hitchcock, Martin Scorsese, Clarence Brown and King Vidor -- tied with Altman at five.
In May, Altman brought out "A Prairie Home Companion," with Keillor starring as the announcer of a folksy musical show -- with the same name as Keillor's own long-running show -- about to be shut down by new owners. Among those in the cast were Meryl Streep, Lily Tomlin, Kevin Kline, Woody Harrelson and Tommy Lee Jones.
"This film is about death," Altman said at a May 3 news conference in St. Paul, Minn., also attended by Keillor and many of the movie's stars.
He often took on Hollywood genres with a revisionist's eye, de-romanticizing the Western hero in 1971's "McCabe and Mrs. Miller" and 1976's "Buffalo Bill and the Indians, or Sitting Bull's History Lesson," the film-noir gumshoe in 1973's "The Long Goodbye" and outlaw gangsters in "Thieves Like Us."
"M-A-S-H" was Altman's first big success after years of directing television, commercials, industrial films and generally unremarkable feature films. The film starring Donald Sutherland and Gould was set during the Korean War but was Altman's thinly veiled attack on U.S. involvement in Vietnam.
"That was my intention entirely. If you look at that film, there's no mention of what war it is," Altman said in an Associated Press interview in 2001, adding that the studio made him put a disclaimer at the beginning to identify the setting as Korea.
"Our mandate was bad taste. If anybody had a joke in the worst taste, it had a better chance of getting into the film, because nothing was in worse taste than that war itself," Altman said.
The film spawned the long-running TV sitcom starring Alan Alda, a show Altman would refer to with distaste as "that series." Unlike the social message of the film, the series was prompted by greed, Altman said.
"They made millions and millions of dollars by bringing an Asian war into Americans' homes every Sunday night," Altman said in 2001. "I thought that was the worst taste."
Altman never minced words about reproaching Hollywood. After the Sept. 11 attacks, he said Hollywood served as a source of inspiration for the terrorists by making violent action movies that amounted to training films for such attacks.
"Nobody would have thought to commit an atrocity like that unless they'd seen it in a movie," Altman said.
Altman was written off repeatedly by the Hollywood establishment, and his reputation for arrogance and hard drinking -- a habit he eventually gave up -- hindered his efforts to raise money for his idiosyncratic films.
While critical of studio executives, Altman held actors in the highest esteem. He joked that on "Gosford Park," he was there mainly to turn the lights on and off for the performers.
The respect was mutual. Top-name actors would clamor for even bit parts in his films. Altman generally worked on shoestring budgets, yet he continually landed marquee performers who signed on for a fraction of their normal salaries.
After the mid-1970s, the quality of Altman's films became increasingly erratic. His 1980 musical "Popeye," with Robin Williams, was trashed by critics, and Altman took some time off from film.
He directed the Broadway production of "Come Back to the Five and Dime, Jimmy Dean, Jimmy Dean," following it with a movie adaptation in 1982. Altman went back and forth from TV to theatrical films over the next decade, but even when his films earned critical praise, such as 1990's "Vincent & Theo," they remained largely unseen.
"The Player" and "Short Cuts" re-established Altman's reputation and commercial viability. But other 1990s films -- including his fashion-industry farce "Ready to Wear" and "Kansas City," his reverie on the 1930s jazz and gangster scene of his hometown -- fell flat.
Born Feb. 20, 1925, Altman hung out in his teen years at the jazz clubs of Kansas City, Mo., where his father was an insurance salesman.
Altman was a bomber pilot in World War II and studied engineering at the University of Missouri in Columbia before taking a job making industrial films in Kansas City. He moved into feature films with "The Delinquents" in 1957, then worked largely in television through the mid-1960s, directing episodes of such series as "Bonanza" and "Alfred Hitchcock Presents."
Altman and his wife, Kathryn, had two sons, Robert and Matthew, and he had a daughter, Christine, and two other sons, Michael and Stephen, from two previous marriages.
When he received his honorary Oscar in 2006, Altman revealed he had a heart transplant a decade earlier.
"I didn't make a big secret out of it, but I thought nobody would hire me again," he said after the ceremony. "You know, there's such a stigma about heart transplants, and there's a lot of us out there."